In spite of the remarkable progress of computational tools in the last decades, integral experiments in zero-power facilities are still of a great importance in the world for nuclear data validation, licensing of new core designs and education and training. Massimo Salvatores was one of the key persons in the promotion of integral experiments and their analysis since the early 1980(s). He initiated many international programs of integral experiments in different zero-power facilities in the world. He expressed a great interest to the integral experiments in the VENUS-F facility that have been performed since 2011 to support ADS MYRRHA and LFR core designs. Some of these experiments and associated calculations are presented in this paper. (C) 2021 Published by Elsevier Ltd.

Today, nuclear power produces 11% of the world's electricity. Nuclear power plants produce virtually no greenhouse gases or air pollutants during their operation. Emissions over their entire life cycle are very low. Nuclear energy's potential is essential to achieving a deeply decarbonized energy future in many regions of the world as of today and for decades to come, the main value of nuclear energy lies in its potential contribution to decarbonizing the power sector. Nuclear energy's future role, however, is highly uncertain for several reasons: chiefly, escalating costs and, the persistence of historical challenges such as spent fuel and radioactive waste management. Advanced nuclear fuel recycling technologies can enable full use of natural energy resources while minimizing proliferation concerns as well as the volume and longevity of nuclear waste. Partitioning and Transmutation (P&T) has been pointed out in numerous studies as the strategy that can relax constraints on geological disposal, e.g. by reducing the waste radiotoxicity and the footprint of the underground facility. Therefore, a special effort has been made to investigate the potential role of P&T and the related options for waste management all along the fuel cycle. Transmutation based on critical or sub-critical fast spectrum transmuters should be evaluated in order to assess its technical and economic feasibility and capacity, which could ease deep geological disposal implementation.

The MYRRHA project started in 1998 by SCK•CEN. MYRRHA is a MTR, based on the ADS concept, for material and fuel research, for studying the feasibility of transmutation of Minor Actinides and Long-Lived Fission Products arising from radioactive waste reprocessing and finally for demonstrating at a reasonable power scale the principle of the ADS. The MYRRHA design has progressed through various framework programmes of the European Commission in the context of Partitioning and Transmutation. The design has now entered into the Front End Engineering Phase (FEED) covering the period 2012-2015. The engineering company, which will handle this phase, has been selected and the works have begun in the late 2013. In the mean time we have made some refinements in both primary systems and plant layout, including reactor building design. In this paper, we present the most recent developments of the MYRRHA design in terms of reactor building and plant layout as existing today as well as a preliminary study concerning the spent fuel building of the facility. During the oral presentation we add some preliminary results of the interaction with the FEED contractor and the most recent version of the primary systems.

The MYRRHA project started in 1998 by SCK•CEN. MYRRHA is an MTR, based on the ADS concept, for material and fuel research, for studying the feasibility of transmutation of Minor Actinides and Long-Lived Fission Products arising from radioactive waste reprocessing and finally for demonstrating at a reasonable power scale the principle of the ADS. The MYRRHA design has progressed through various framework programmes of the European Commission in the context of Partitioning and Transmutation. The design has now entered into the Front End Engineering Phase (FEED) covering the period 2012–2015. The engineering company, which will handle this phase, has been selected and the works have begun in the late 2013. In the mean time we have made some refinements in both primary systems and plant layout, including the reactor building design. In this paper, we present the most recent developments of the MYRRHA design as existing today.

MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is a multi-purpose research facility currently being developed at SCK•CEN. It will be able to work in both critical and sub-critical modes and, cooled by lead-bismuth eutectic. It will play a key role in the development of the Pb-alloy technology needed for the lead fast reactor GEN IV concept. MYRRHA will demonstrate the Accelerator Driven System (ADS) full concept by coupling a proton accelerator, a spallation target and a sub-critical reactor at a reasonable power level to allow operation feedback. MYRRHA will also contribute to the study of partitioning and transmutation of high-level waste. Recently, a new core design with a longer active core has been proposed. This paper presents the neutronic analyses for this design improvement. The analyses have been done using the MCNP/X code and the in-house developed ALEPH2 depletion code.

The GUINEVERE project was launched in 2006, within the 6th Euratom Framework Program IP-EUROTRANS, in order to study the feasibility of transmutation in Accelerator Driven subcritical Systems (ADS). This zero-power facility hosted at the SCK·CEN site in Mol (Belgium) couples the fast subcritical lead reactor VENUS-F with an external neutron source provided by interaction of deuterons delivered by the GENEPI-3C accelerator and a tritiated target located at the reactor core center. In order to test on-line subcriticality monitoring techniques, the reactivity of all the VENUS-F configurations used must be known beforehand to serve as benchmark values. That is why the Modified Source Multiplication Method (MSM) is under consideration to estimate the reactivity worth of the control rods when the reactor is largely subcritical as well as near-critical. The MSM method appears to be a technique well adapted to measure control rod worth over a large range of subcriticality levels. The MSM factors which are required to account for spatial effects in the reactor can be successfully calculated using a Monte Carlo neutron transport code.

Within the FREYA Project, methods to interpret flux measurements in the VENUS-F core are being studied in order to reconstruct the subcriticality level of the facility. In this work, after the presentation of results obtained with standard techniques such as the Area Method, we introduce an alternative approach to the experimental determination of the reactivity. This method, whose validity has been tested by computational exercises, makes use of general mathematical properties of the point kinetics system of equations and has been recently extended for subcritical system analysis. The evaluation of spatial correction factors is also carried out using deterministic transport evaluations (ERANOS code). The statistical and systematic uncertainty of the results in terms of reactivity is discussed and numerical results are presented

The evaluation of experimental techniques for the determination of the subcriticality level of an ADS core relies on reactor point kinetics. The measured parameters depend on the detector position, and the reactivity values are subject to spatial correction factors (SCFs). In this paper the contribution of different eigenmodes to the SCF for the pulsed neutron source (PNS) technique is assessed. Moreover by pulse simulations, precise values of the correction factor are obtained.As case study, the VENUS-F SC1 subcritical core is investigated, with a pulsed neutron source in the center of the core, generated by the GENEPI-3C deuteron accelerator. Much more than 100 modes need to be taken into account to precisely obtain the spatial correction factor for the area method evaluation of this core. Especially the modes with a maximum in the center of the core contribute significantly to the SCF. No spatial correction needs to be applied close to the zeros of the first mode with a maximum in the center of the core (different from the fundamental one). In the reflector zone, the absolute reactivity level is overestimated. (C) 2014 Elsevier Ltd. All rights reserved.

In order to guarantee a sufficient margin to criticality and a precise follow-up of the burn-up of the reactor fuel, the monitoring of subcriticality during all phases of operation of an ADS is indispensable. For this purpose, the GUINEVERE [1] and FREYA [2] projects were launched to set-up and test a methodology for robust reactivity monitoring of an ADS, in support of the MYRRHA demonstrator [3].

MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is a multipurpose research facility currently being developed at SCK•CEN. MYRRHA is based on the ADS (Accelerator Driven System) concept where a proton accelerator, a spallation target and a subcritical reactor are coupled. MYRRHA will demonstrate the ADS full concept by coupling these three components at a reasonable power level to allow operation feedback. As a flexible irradiation facility, the MYRRHA research facility will be able to work in both critical as subcritical modes. In this way, MYRRHA will allow fuel developments for innovative reactor systems, material developments for GEN IV and fusion reactors, and radioisotope production for medical and industrial applications. MYRRHA will be cooled by lead-bismuth eutectic and will play an important role in the development of the Pb-alloys technology needed for the LFR (Lead Fast Reactor) GEN IV concept. MYRRHA will also contribute to the study of partitioning and transmutation of high-level waste. Transmutation of minor actinides (MA) can be completed in an efficient way in fast neutron spectrum facilities, so both critical reactors and subcritical ADS are potential candidates as dedicated transmutation systems. However critical reactors heavily loaded with fuel containing large amounts of MA pose reactivity control problems, and thus safety problems. A subcritical ADS operates in a flexible and safe manner, even with a core loading containing a high amount of MA leading to a high transmutation rate. In this paper, the most recent developments in the design of the MYRRHA facility are presented.

In order to incinerate minor actinides and thus to reduce the issues linked to nuclear waste management, Accelerator-Driven Systems (ADS) are being under study. An ADS consists in the coupling of a particle accelerator with a sub-critical fast reactor. The on-line reactivity monitoring is a serious issue regarding safety, therefore several methods to estimate the reactivity of such sub-critical systems have to be investigated. Here, we present one method based on the study of the neutron population evolution during beam interruption experiments carried out in the framework of the FREYA FP7 program [1,2] at the GUINEVERE facility, which couples the fast lead sub-critical reactor VENUS-F with the deuteron accelerator GENEPI-3C at SCK-CEN in Mol, Belgium. After describing the facility, the analysis based on point kinetics theory and preliminary results of the reactivity measurements will be presented. Then, spatial effects that are not taken into account by point kinetics theory will be highlighted using MCNP simulations, and correction factors to raw results will be calculated. In the end, final results will be compared to reference reactivity values obtained with the Modified Source Multiplication (MSM) method.

MYRRHA (multi-purpose hybrid research reactor for high-tech applications) is a multipurpose research facility currently being developed at SCK-CEN. It will be able to work in both critical and subcritical modes and, cooled by lead-bismuth eutectic. In this paper the minor actinides (MA) transmutation capabilities of MYRRHA are investigated. (Pu + Am, U) MOX fuel and (Np + Am + Cm, Pu) Inert Matrix Fuel test samples have been loaded in the central channel of the MYRRHA critical core and have been irradiated during five cycles, each one consisting of 90 days of operation at 100 MWth and 30 days of shutdown. The reactivity worth of the test fuel assembly was about 1.1 dollar. A wide range of burn-up level has been achieved, extending from 42 to 110 MWd/kg HM, the samples with lower MA-to-Pu ratios reaching the highest burn-up. This study has highlighted the importance of the initial MA content, expressed in terms of MA/Pu ratio, on the transmutation rate of MA elements. For (Pu + Am, U) MOX fuel samples, a net build-up of MA is observed when the initial content of MA is very low (here, 1.77 wt% MA/Pu) while a net decrease in MA is observed in more » the sample with an initial content of 5 wt%. This suggests the existence of some 'equilibrium' initial MA content value beyond which a net transmutation is achievable. « less

On April 2009, a three-year-project was launched within the 7th Framework Programme (FP) of the European Commission: the Central Design Team (CDT) for a FAst Spectrum Transmutation Experimental Facility (FASTEF). The main goal was to achieve an advanced level of design for an irradiation facility, cooled by lead-bismuth, operating in both critical and sub-critical modes. In continuity with the research studies on fast nuclear systems carried out in the 5-6th FPs, the CDT had the further ambitious objective to define a preliminary design of the MYRRHA reactor, planned to be built at the SCK.CEN research centre in Mol (Belgium). In addition to being a multi-purpose irradiation facility, MYRRHA should be able to demonstrate the Acceleration Driven System concept at 100 MW power level and an efficient transmutation of minor actinides, as main contributors to high-level long-lived radioactive wastes.This paper describes the design of cores able to operate the MYRRHA-FASTEF plant in both critical and sub-critical modes. The design studies were performed by detailed neutronic analyses (with deterministic and Monte Carlo methods) and by accurate thermal-hydraulic evaluations (at the fuel assembly and pin sub-channel level), by taking also into account thermo-mechanical and safety constraints. Among the most significant core features, the fast flux level (Phi(>0.75 MeV) similar to 10(15) Cm-2 S-1), the high flexibility for irradiation purposes and the limited overall dimension (impacting on the cost of the plant) can be noticed. The transmutation of minor actinides, enhanced by the high fast flux, reaches values of about 32 kg(HM) TWh(-1) in both operational modes. (C) 2013 Elsevier B.V. All rights reserved.

Reactor physics experiments are required for the design of a Fast Spectrum Transmutation Experimental Facility MYRRHA/FASTEF working in subcritical mode and in critical mode. Reactor physics experiments aim to validate a methodology for on-line subcriticality monitoring. For this purpose, building on the former activities accomplished in the previous FP6 project GUINEVERE, investigations on the subcritical VENUS-F (lead/uranium) cores coupled with the GENEPI-3C accelerator will be extended. This activity has been planned in within the framework of the on-going FREYA (Fast Reactor Experiments for hYbrid Applications) FP7 project. This paper presents the current progress of the project and the future plans.

The GUINEVERE (Generation of Uninterrupted Intense NEutron pulses at the lead VEnus REactor) project was launched in 2006 within the framework of FP6 EUROTRANS in order to validate online reactivity monitoring and subcriticality level determination in accelerator driven systems (ADS). Therefore, the VENUS reactor at SCK-CEN in Mol, Belgium, was modified towards a fast core (VENUS-F) and coupled to the GENEPI-3C accelerator built by CNRS. The accelerator can operate in both continuous and pulsed mode. The VENUS-F core is loaded with enriched Uranium and reflected with solid lead. A well-chosen critical reference state is indispensable for the validation of the online subcriticality monitoring methodology. Moreover, a benchmarking tool is required for nuclear data research and code validation. In this paper, the design and the importance of the critical reference state for the GUINEVERE project are motivated. The results of the first experimental phase on the critical core are presented. The control rods worth is determined by the positive period method and the application of the Modified Source Multiplication (MSM) method allows the determination of the worth of the safety rods. The results are implemented in the VENUS-F core certificate for full exploitation of the critical core.

MYRRHA (Multi-purpose hYbrid Research Reactor for High-tech Applications) is the flexible experimental Accelerator-Driven System (ADS) currently under development at SCK.CEN and will replace the Material Testing Reactor (MTR) BR2. The MYRRHA facility is currently being developed with the aid of the FP7-project "Central Design Team" and will be as a flexible irradiation facility, able to work in both subcritical and critical modes. In this way, MYRRHA will allow fuel developments for innovative reactor systems, material developments for GEN IV systems, material developments for fusion reactors, radioisotope production for medical and industrial applications, and Si-doping. MYRRHA will also demonstrate the full concept of Accelerator Driven Systems by coupling the requisite three components (accelerator, spallation target and subcritical reactor) at reasonable power level to allow operation feedback, scalable to an industrial demonstrator and allow for the study of efficient transmutation of high-level nuclear waste. Since MYRRHA is based on the heavy liquid metal technology, Lead-Bismuth Eutectic, it will be able to significantly contribute to the development of Lead Fast Reactor (LFR) technology. Further, in critical mode, MYRRHA will play the role of European Technology Pilot Plant in the path forward for LFR. In this paper we present the historical perspectives, international and high profile membership within the consortium of the MYRRHA project and the rationale for the design choices are presented. Also, the latest configuration of the reactor system is described together with the different irradiation capabilities. More specifically, the possibilities and performances for fuel irradiations are presented in detail. (C) 2012 Elsevier Ltd. All rights reserved.

The Monte-Carlo burn-up code ALEPH is being developed at SCK-CEN since 2004. A previous version of the code implemented the coupling between the Monte Carlo transport (any version of MCNP or MCNPX) and the ' deterministic' depletion code ORIGEN-2.2 but had important deficiencies in nuclear data treatment and limitations inherent to ORIGEN-2.2. A new version of the code, ALEPH2, has several unique features making it outstanding among other depletion codes. The most important feature is full data consistency between steady-state Monte Carlo and time-dependent depletion calculations. The last generation general-purpose nuclear data libraries (JEFF-3.1.1, ENDF/B-VII and JENDL-4) are fully implemented, including special purpose activation, spontaneous fission, fission product yield and radioactive decay data. The built-in depletion algorithm allows to eliminate the uncertainties associated with obtaining the time-dependent nuclide concentrations. A predictor-corrector mechanism, calculation of nuclear heating, calculation of decay heat, decay neutron sources are available as well. The validation of the code on the results of REBUS experimental program has been performed. The ALEPH2 has shown better agreement with measured data than other depletion codes. (authors)